As a whole, mitochondrial diseases are among the most common hereditary diseases. They can arise from mutations of nuclear or mitochondrial (mtDNA) genes that encode for components of the oxidative phosphorylation (OXPHOS) machinery. It is clear that mitochondria have to constantly adapt to changes in substrate availability and energy utilization by modulating OXPHOS to maintain cellular ATP supplies. However, very little is known on how cells with mitochondrial genetic defects regulate OXPHOS or how they attempt to compensate for their biochemical defects. Short-term OXPHOS regulation is modulated by reversible phosphorylation of mitochondrial enzymes. A mitochondrial cAMP-Protein kinase A (cAMP-PKA) pathway has been hypothesized, but the source of cAMP in mitochondria has remained elusive. We have recently found that the mitochondrial cAMP pool is generated by a soluble adenylyl cyclase (sAC) in response to metabolically generated CO2. This novel CO2-sAC-cAMP-PKA signaling cascade is entirely contained within mitochondria and operates as a metabolic sensor modulating ATP production in response to nutrients availability. We showed that OXPHOS defective cells have a different regulation of the sAC-cAMP-PKA pathway as compared to wild type cells, suggesting that the pathway may participate to the adaptive responses to OXPHOS defects. Thus, this pathway could become a novel target for therapeutic intervention in mitochondrial diseases. To test these hypotheses we propose to search for specific protein targets of the CO2-sAC-cAMP-PKA signaling pathway in mitochondria focusing on enzymes of the Krebs cycle and the electron transfer chain. Then, once these targets are identified, we will assess the differences in protein phosphorylation between wild type and mutant cells. The goals of this application are: 1) To identify sAC-cAMP-PKA targets implicated in OXPHOS regulation and 2) to investigate the molecular mechanisms underlying OXPHOS regulation by the mitochondrial sAC-cAMP-PKA pathway in OXPHOS deficient cells.